The development of hyperthermia as a practical cancer treatment has been hindered by difficulties in reliably heating small visceral masses. Current non-invasive techniques (ultrasound, microwaves, radiofrequency current, whole-body hyperthermia) do not permit the selective treatment of visceral masses less than 5 cm diameter, and many masses larger than this cannot be heated either. We have investigated an invasive hyperthermia technique utilizing ferromagnetic seeds. These are composed of a nickel-copper alloy of our own manufacture, and have a Curie Point of 51 C. These seeds can be surgically implanted into a tumor and, when exposed to an oscillating magnetic field, heat up to the Curie Point and stablize at that temperature. These seeds can be expected to produce good temperature homogeneity throughout the tumor volume and only moderate heating of adjacent tissues. The proposed studies are directed toward developing an adequate clinical foundation for eventual human studies with these thermoseeds. The studies will consist of toxicologic and clinical investigations as well as some developmental engineering work. 1. An adequeate number of thermoseeds will need to be produced for the animal studies. This will involve wire manufacture, annealing, and electroplating the seeds. 2. A magnetic induction system will be developed. The proposed system will permit the field to be oriented in any direction with respect to the body axis, and thereby allow great flexibility in thermoseed implantation. 3. Toxicologic investigations in rats will examine possible dissolution of the thermoseeds during prolonged body contact. 4. Phase I studies of hyperthermia alone, and hyperthermia with radiation, will be conducted in dogs with spontaneous and implanted tumors. The reproducibility and toxicity of heating with the thermoseeds will be examined.